1. Field of the Invention
The present invention relates to systems and methods of water purification, and, more particularly, the control of nutrients, suspended and filamentous algae, pollutants, and toxins in bodies of water.
2. Description of Related Art
Many freshwater lakes and ponds, as well as estuaries, are characterized, particularly during the warmer months, by a significant population of suspended algae or phytoplankton in the water body's water column. These largely unicellular plants give the water a greenish and often a “pea-soup” appearance that many observers find unattractive. Floating mats of unsightly, filamentous algae also can occur. High concentrations of algae may lead to low levels of dissolved oxygen in the early morning hours, leading to stress on the aquatic and fish populations. In extreme cases, these conditions will lead to fish kills and the general decline of the quality of a water body.
The basis of the problem is an abundance of soluble nutrients within the water body, which then allows the rapid growth and maintenance of the elevated population of suspended or filamentous algae. The source of the soluble nutrients may be sediments, air deposition, point source polluting discharges, generalized, non-point-source inflows, or most likely a combination of all these factors. An effective management strategy would combine elements of attempting to reduce nutrient loading to the water bodywith treatment of the water body itself.
Currently used methods of controlling algal growth in ponds or lakes typically involve treating the water with selected herbicides or “algicides.” These chemicals kill the suspended algae, returning the water to its more desired appearance of clear or only slightly colored waters. Another strategy employed in managing algae is to introduce a dye that then, via the mechanism of shading, achieves the same result of killing the algae and returning the water to its algae-free appearance.
A problem with these approaches is that the underlying feature that initially encouraged the growth of the algae remains; that is, the nutrients on which the algae grew remain in the water, and after the effects of the algicide, herbicide, or dye decrease, the conditions for a renewed growth of algae are abundantly present. In addition, for the algicide and herbicide at least, the negative environmental effects of potentially toxic accumulation must be considered.
An alternative strategy to killing the algae and then creating relatively clear but nutrient-rich water body is to employ technologies that remove these nutrients from the water body. A natural method of achieving this nutrient removal is through the harvesting of macrophyte vegetation, which takes up the soluble nutrients as a function of their growth. If the total mass of nutrients removed through plant harvest were to match the ongoing nutrient loading through the various sources of sediment transport, air deposition point and nonpoint sources, then the lake or pond would be able to maintain an algal-free appearance. Another alternative approach is to immobilize water column phosphorus by adding a chemical coagulant, such as aluminum sulfate.
Another site of contaminated water is the so-called “waste stabilization pond” (WSP), a body of water used to store industrial, municipal, agricultural wastewater or contaminated groundwater. The WSP is believed to be the most prevalent type of wastewater treatment technology in the world. There is an immediate need to enhance the pollutant removal effectiveness of most WSPs.